In javascript:

x == x _ is true. Good.

x == !x _ is also true. Oops?

And guess what:

Array(3)==",," _ is also true.

But

NaN == NaN _ is false.

Math.max()>Math.min() _ is also false!

but then again

Math.max()<Math.min() _ is true.

Madness, I tell you!

NaN not being equal to itself is true in all languages with IEEE compliance: https://en.wikipedia.org/wiki/NaN

Nitpick: NaN is supposed to work like that: the rule is that every comparison of any value against NaN returns false.

I just looked at the famous left-pad for the fastest way o implementing a pad function in JS.

I asked a friend that does web dev and it is apparently pretty idiomatic JS. Pretty appalling. I finally understood why people claimed it was "hard to get right".

:D Many more Javascript WTF's here: https://www.youtube.com/results?search_query=javascript+wtf

At least x === x, right?

const x = NaN;

x === x; // false

But they're close to getting two numbers to add together!

https://twitter.com/thomasfuchs/status/933447631514169344

They should use jQuery for that. I hear it's good for all the things.